1. Field of the Invention
The present invention relates to magnetic sensors in which electrode layers are formed to overlap a multilayer film, and more particularly, relates to a magnetic sensor in which overlap electrode layers at the left and right sides can be precisely formed so that the film thicknesses thereof are equivalent to each other.
2. Description of the Related Art
FIG. 21 is a partly cross-sectional view of a related magnetic sensor (spin-valve type thin-film element) viewed from an opposing face side opposing a recording medium.
Reference numeral 1 indicates a first antiferromagnetic layer composed of a PtMn alloy or the like, and on this first antiferromagnetic layer 1, a fixed magnetic layer 2 formed of a NiFe alloy or the like, a nonmagnetic material layer 3 formed of Cu or the like, and a free magnetic layer 4 formed of a NiFe alloy or the like are provided to form a laminate structure.
As shown in FIG. 21, on the free magnetic layer 4, second antiferromagnetic layers 5 with a track width Tw provided therebetween in the track width direction (X direction in the figure) are formed, and on these second antiferromagnetic layers 5, electrode layers 6 are provided.
In the embodiment shown in FIG. 21, exchange coupling magnetic fields are generated in regions in which the second antiferromagnetic layers 5 are provided on the free magnetic layer 4, the magnetizations of the free magnetic layer 4 in the regions described above are fixed in the X direction shown in the figure, and the free magnetic layer 4 in the track width Tw is put in a weak single domain state so that the magnetization reverse may occur with respect to an external magnetic field.
In the related example shown in FIG. 21, there have been the following two problems. The first problem is that element resistance cannot be satisfactory decreased. The reason for this is that the second antiferromagnetic layer 5 is formed of a material such as a PtMn alloy having a high resistivity, and that sense current flows from the electrode layer 6 to the free magnetic layer 4 side through this second antiferromagnetic layer 5 (the flow of the sense current is shown by the arrows). The PtMn alloy mentioned above has a resistivity of an approximately 170 xcexcxcexa9xc2x7cm or more, and on the other hand, the electrode layer 6 is formed of a material such as Au having a very low resistivity of approximately 2 to 6 xcexcxcexa9xc2x7cm. Hence, even when a material having a low resistivity is used for the electrode layer 6, according to the structure of the magnetic sensor shown in FIG. 21, the sense current must flow once through the second antiferromagnetic layer 5 having a high resistivity, and as a result, decrease in element resistance cannot be achieved. In addition, since the element height has been decreased concomitant with recent trend toward higher recoding density, the element resistance is also increased.
The second problem is side reading. As described above, since flowing toward the free magnetic layer 4 side through the second antiferromagnetic layer 5, the sense current spreads wider than the track width Tw and then flows toward the free magnetic layer 4 side. In this step, since the magnetization of the free magnetic layer 4 in the vicinity of the track width Tw is not tightly fixed with the second antiferromagnetic layer 5 and varies to some extent with respect to an external magnetic field, a so-called effective track width tends to be larger than the track width Tw (this track width Tw is also referred to as xe2x80x9coptical track widthxe2x80x9d in some cases) shown in the figure. Consequently, the side reading is liable to occur in that external signals are read at positions apart from the track width Tw.
In order to solve the above two problems, the structure in which the electrode layers 6 overlaps the free magnetic layer 4 in the track width Tw has been researched.
FIGS. 22 and 24 are views showing steps of manufacturing a magnetic sensor in which electrode layers form an overlap structure. The views showing the manufacturing steps, described above, are partly cross-sectional views each showing a magnetic sensor in the manufacturing step when viewed from an opposing face side opposing a recording medium.
In the step shown in FIG. 22, the first antiferromagnetic layer 1, the fixed magnetic layer 2, the nonmagnetic material layer 3, and the free magnetic layer 4 are formed in that order from the bottom, and in addition, on the free magnetic layer 4, the second antiferromagnetic layers 5 are formed with a predetermined space T1 provided therebetween in the track width direction (X direction in the figure). For the formation of the second antiferromagnetic layers 5, as shown in FIG. 22, for example, a solid second antiferromagnetic film 5 is first formed over the entire surface of the free magnetic layer 4, resist layers 8 with a predetermined space therebetween in the track width direction are formed on the solid second antiferromagnetic film 5, part of the solid second antiferromagnetic film 5 which is not covered with the resist layers 8 is removed by etching, and the resist layers 8 are then removed, thereby forming the second antiferromagnetic layers 5.
In the step shown in FIG. 23, a solid electrode film 6 is formed on the second antiferromagnetic layers 5 and the free magnetic layer 4, and on the solid electrode film 6, a resist film 7 is formed. In the step shown in FIG. 23, a space for the track width Tw is formed in the resist film 7 in the track width direction (X direction in the figure), thereby forming the resist layers 7. The track width Tw is smaller than the space T1 formed between the second antiferromagnetic layers 5.
In the step shown in FIG. 24, part of the solid electrode film 6 which is not covered with the resist layers 7 is removed by ion milling or reactive ion etching, thereby exposing the upper surface of the free magnetic layer 4. Since the other parts of the solid electrode film 6, which are not removed and which form the electrode layers 6, overlap the upper surfaces of the second antiferromagnetic layers 5 and the free magnetic layer 4, and sense current tends to flow easily from the electrode layers 6 to the free magnetic layer 4 side (the flow of the sense current is indicated by the arrows in FIG. 24), it has been anticipated that the problems described above, that is, the increase in element resistance and the side reading, can be simultaneously solved.
In recent years, the track width TW has been decreased concomitant with the trend toward higher recording density. When the track width Tw is decreased, dead regions (regions which do not directly contribute to reproduction) positioned under the second antiferromagnetic layers 5 and in the very vicinity of both sides of the track width tend to have a larger ratio of the whole area, and as a result, decrease in reproduction output cannot be prevented. However, when the structure is formed so that the electrode layers 6 overlap the free magnetic layer by the manufacturing steps shown in FIGS. 22 to 24, the dead regions can be decreased to some extent as compared to those of the magnetic sensor shown in FIG. 22 since the space between the second antiferromagnetic layers 5 can be increased, and hence it has been expected that the reproduction output can be effectively improved by the structure described above.
In addition, in the structure in which the electrode layers 6 overlap the free magnetic layer 4 while the track width Tw is decreased, as is the magnetic sensor shown in FIG. 24, widths T2 and T3 (hereinafter referred to as xe2x80x9coverlap lengthxe2x80x9d) of the overlap portions in the track width direction are approximately {fraction (1/100)}xcexcm, and hence the alignment accuracy becomes important when the electrode layers 6 are formed.
However, in the manufacturing steps shown in FIGS. 22 to 24, the second antiferromagnetic layers 5 each having a predetermined shape are first formed using the resist layers 8 in the step shown in FIG. 22, and after the resist layers 8 are removed, in the step shown in FIG. 23, the overlap structure must be formed by the electrode layers 6 again using the resist layers 7.
That is, mask alignment must be performed at least twice, and since the alignment accuracy is approximately xc2x1{fraction (1/100)}xcexcm for forming the resist layers 7, when the alignment is deviated by only approximately {fraction (1/100)}xcexcm, the overlap lengths T2 and T3 of the electrode layer 6 at both sides are not equivalent to each other and become significantly different from each other. In addition, in the worst case, one of the electrode layers 6 may be formed so as to overlap the free magnetic layer 4, and the other electrode layer 6 may be formed only on the second antiferromagnetic layer 5 and may not overlap the free magnetic layer 4.
As described above, in the past, it has been considered that the increase in element resistance and the generation of side reading can be suppressed by forming the electrode layers 6 so as to overlap the free magnetic layer 4. However, when the magnetic sensor is actually manufactured, it has been difficult to form equivalent overlap lengths of the electrode layers formed at the left and the right sides since mask alignment must be performed twice, and as a result, the generation of side reading and the increase in element resistance could not be effectively suppressed by the magnetic sensor in which the overlap lengths of the electrode layers at the left and the right are different from each other.
Accordingly, the present invention was made in order to solve the problems described above, and particularly, an object of the present invention is to provide a magnetic sensor having an overlap structure, in which overlap electrode layers at the left and the right sides have shapes equivalent to each other, and a manufacturing method thereof. The overlap structure mentioned above can be obtained by forming the overlap electrode layers described above separately from electrode layers provided on second antiferromagnetic layers.
A magnetic sensor according to the present invention, which has a multilayer film formed of a first antiferromagnetic layer, a fixed magnetic layer, a nonmagnetic material layer, and a free magnetic layer provided in that order from the bottom, comprises: second antiferromagnetic layers which are disposed with a predetermined space provided therebetween in the track width direction and which are provided on the upper surface of the multilayer film; first electrode layers formed on the respective second antiferromagnetic layers; and second electrode layers disposed with a predetermined space provide therebetween in the track width direction, the second electrode layers being provided directly on or indirectly above at least internal end surfaces in the width direction of the first electrode layers and the second antiferromagnetic layers and parts of the upper surface of the multilayer film.
In the present invention, the first electrode layers are preferably formed in a step separate from that for the second electrode layers.
In the present invention, as described above, the first electrode layers are formed on the second antiferromagnetic layers formed with a predetermined space provided therebetween in the track width direction. In a separate step from that for the first electrode layers, the second electrode layers are formed directly on or indirectly above the internal end surfaces of the first electrode layers and the second antiferromagnetic layers and parts of the upper surface of the multilayer film. That is, the second electrode layers each directly or indirectly overlap the upper surface of the multilayer film.
According to one embodiment of the present invention, since the second electrode layers at the left and the right sides can be formed so as to symmetrically overlap the upper surface of the multilayer, decrease in element resistance and reduction of side reading can be effectively achieved even when the track has been narrowed. In addition, the reproduction output can be more effectively improved as compared to that in the past.
In the present invention, since the first electrode layers are formed in a step separate from that for the second electrode layers, the first electrode layers may be formed of a material different from that for the second electrode layers. As a result, for example, the first electrode layers may be formed of a material having ductility lower than that of the second electrode layers.
When the first electrode layer and the second electrode layer are both formed of a soft material, such as Au, having high ductility, and when polishing is performed in a slider-forming step or the like, smearing occurs, and hence short circuiting occurs between the electrode layer and an upper shield layer or a lower shield layer, resulting in destruction of reproduction functions of the magnetic sensor. It is important that the second electrode layers forming the overlap structure have high conductivity, and according to the structure of the present invention, even when the first electrode layer has conductivity lower than that of the second electrode layer, the reproduction characteristics are not so much degraded. In addition, the area in which the first electrode layer is formed tends to be larger than that in which the second electrode layer is formed. Accordingly, when the first electrode layer is formed of a material having ductility lower than that of the second electrode layer, the generation of smearing can be effectively suppressed.
In the present invention, the first electrode layer is preferably formed of at least one of Cr, Rh, Ru, Ta, and W, or an alloy of Au containing at least one of Pd and Cr, and the second electrode layer is preferably formed of at least one of Au, Cu, and Ag.
In addition, in the present invention, the second electrode layers are preferably formed only on the internal end surfaces and the parts of the upper surface of the multilayer film.
In the present invention, stop layers are preferably provided under the second electrode layers and are preferably composed of a material having an etching rate lower than that of the second electrode layers.
The stop layers are preferably formed of at least one element selected from the group consisting of Ta, Cr, V, Nb, Mo, W, Fe, Co, Ni, Pt, and Rh. The stop layers each preferably have a laminate structure composed of a Cr layer and a Ta layer provided in that order from the bottom.
In the present invention, the internal end surfaces of the second antiferromagnetic layers and the respective internal end surfaces of the first electrode layers preferably form continuous surfaces.
A method for manufacturing a magnetic sensor, according to the present invention, comprises the following steps. The steps are: step (a) of forming a multilayer film including a first antiferromagnetic layer, a fixed magnetic layer, a nonmagnetic material layer, and a free magnetic layer provided in that order on a substrate; step (b) of forming second antiferromagnetic layers, which are disposed on two side portions of the multilayer film in the track width direction, and first electrode layers on the second antiferromagnetic layers; and step (c) of forming second electrode layers directly on or indirectly above at least internal end surfaces in the track width direction of the first electrode layers and the second antiferromagnetic layers and parts of the upper surface of the multilayer film, the second electrode layers being provided with a predetermined space provided therebetween in the width direction.
According to steps (a) to (c), the first electrode layers and the second electrode layers can be formed in separate steps, and since it is not necessary to perform mask alignment twice as was in the past, an overlap structure can be precisely formed in which overlap lengths, which are the thickness of the electrodes, at the left and the right sides are equivalent to the other.
According to the present invention, a method for manufacturing a magnetic sensor, comprises: step (a) of forming a multilayer film including a first antiferromagnetic layer, a fixed magnetic layer, a nonmagnetic material layer, and a free magnetic layer provided in that order on a substrate; step (b) of forming second antiferromagnetic layers, which are disposed on two side portions of the multilayer film in the track width direction, and first electrode layers on the second antiferromagnetic layers; step (d) of forming a solid second electrode film on the upper surfaces of the first electrode layers, internal end surfaces in the track width direction of the first electrode layers and the second antiferromagnetic layers, and the upper surface of the multilayer film; and step (e) of removing a center part of the solid second electrode film formed on the upper surface of the multilayer film, whereby second electrode layers with a predetermined space provided therebetween in the track width direction are formed on the internal end surfaces and parts of the upper surface of the multilayer film.
In steps (d) and (e), mask alignment of a resist performed in the past is not necessary, and the second electrode layers can be formed in a step separate from that for the first electrode layers so that the overlap lengths at the left and the right sides are equivalent to each other.
The method for manufacturing a magnetic sensor, according to the present invention, may further comprise forming a solid stop film on the upper surfaces of the first electrode layers, the internal end surfaces in the track width direction of the first electrode layers and the second antiferromagnetic layers, and the upper surface of the multilayer film after step (b) is performed; and after a part of the solid stop film is exposed by removing the center part of the solid second electrode film in step (e), removing the part of the solid stop film.
In the present invention, the solid stop film is preferably formed of a material having an etching rate lower than that of the solid second electrode film. In particular, the solid stop film is preferably formed of at least one element selected from the group consisting of Ta, Cr, V, Nb, Mo, W, Fe, Co, Ni, Pt, and Rh. In addition, the solid stop film is more preferably formed of a Cr layer and a Ta layer provided in that order from the bottom.
When the center part of the solid second electrode film formed on the multilayer film is removed in step (e), the multilayer film may be damaged by overetching in some cases in this step. Accordingly, in the case in which the solid stop film is provided in order to avoid the damage described above, even when the solid second electrode film formed on the solid stop film is removed by etching, and over etching is then further performed, the multilayer film is prevented from being damaged by the etching.
In the present invention, it is preferable that the solid second electrode film provided on the upper surfaces of the first electrode layers be entirely removed in step (e).
In the present invention, in step (d), the solid second electrode film is preferably formed by sputtering with a sputtering angle inclined from the direction perpendicular to the substrate so that the thickness thereof on the internal end surfaces is larger than each of those on the upper surface of the multilayer film and on the upper surfaces of the first electrode layers.
The difference in thickness at the individual positions of the solid second electrode film formed by sputtering is significantly important. As described above, when the solid second electrode film is sputtered, the thickness thereof on the internal end surfaces must be larger than each of those on the upper surface of the multilayer film and on the upper surfaces of the first electrode layers.
In step (e), the center part of the solid second electrode film, which is formed on the upper surface of the multilayer film with or without another layer provided therebetween, is removed, and in this step, parts of the solid second electrode film formed on the internal end surfaces are also removed. However, in the present invention, the solid second electrode film formed on the internal end surfaces must remain for forming the second electrode layers. Accordingly, when the thickness of the solid second electrode film on the internal end surfaces is smaller than that on the upper surface of the multilayer film, before the solid second electrode film on the upper surface of the multilayer film is entirely removed, the solid second electrode film formed on the internal end surfaces may be removed faster than that described above in some cases. Hence, in the present invention, the solid second electrode film, which is to be formed into the second electrode layers, is formed by sputtering with a sputtering angle inclined from the direction perpendicular to the substrate, and as a result, the thickness of the solid second electrode film on the internal end surfaces is larger than each of those on the upper surface of the multilayer film and on the upper surfaces of the first electrode layers.
In the present invention, when the solid second electrode film is formed in step (d), the thickness thereof on the upper surface of the multilayer film is preferably smaller than each of those on the upper surfaces of the first electrode layers.
In the present invention, in step (e) of removing the center part of the solid second electrode film formed on the upper surface of the multilayer film by milling, the milling angle is preferably set close to perpendicular to the substrate as compared to the sputtering angle used for forming the solid second electrode film.
Accordingly, since the center part of the solid second electrode film can be appropriately removed, the second electrode layers having a predetermined thickness can be formed on the internal end surfaces, and hence the overlap structure can be precisely formed in which the thicknesses of the second electrode layers at the left side and the right side are equivalent to each other.
In addition, in the present invention, the first electrode layers are preferably formed of a nonmagnetic conductive material different from that for the second electrode layers. Furthermore, the first electrode layers are preferably formed of a material having ductility lower than that for the second electrode layers.
In the present invention, the first electrode layers are preferably formed of at least one of Cr, Rh, Ru, Ta, and W, or an alloy of Au containing at least one of Pd and Cr, and the second electrode layers are preferably formed of at least one of Au, Cu, and Ag.